A fluid ejection system typically includes a fluid path from a fluid supply to a nozzle assembly that includes nozzles from which fluid drops are ejected. Fluid drop ejection can be controlled by pressurizing fluid in the fluid path with an actuator, such as a piezoelectric actuator. The fluid to be ejected can be, for example, an ink, electroluminescent materials, biological compounds, or materials for formation of electrical circuits.
A printhead module in an ink jet printer is an example of a fluid ejection system. A printhead module typically has a line or an array of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled by one or more controllers. The printhead module can include a semiconductor printhead body in which the ink paths are formed and piezoelectric actuators attached to the printhead body. A nozzle can be defined by a separate layer that is attached to the printhead body. The printhead body can be made of a silicon substrate etched to define a pumping chamber along an ink path.
One side of the pumping chamber is a membrane that is sufficiently thin to flex and expand or contract the pumping chamber when driven by the piezoelectric actuator. The piezoelectric actuator is supported on the membrane over the pumping chamber. The piezoelectric actuator includes a layer of piezoelectric material that changes geometry (or actuates) in response to a voltage applied across the piezoelectric layer by a pair of opposing electrodes. The actuation of the piezoelectric layer causes the membrane to flex, and the flexing of the membrane thereby pressurizes ink in the pumping chamber along the ink path and eventually ejects an ink droplet out of the nozzle.
As a printhead module gets smaller, so do the pumping chambers and corresponding actuators, but smaller actuators eject smaller drops (e.g., 5 pL or less). Small drops are desirable when printing resolutions around 1200 dpi, but smaller drops may not work well when printing lower resolutions, such as around 600 dpi. To print at 600 dpi resolution, bigger drops are necessary (e.g., 9-10 pL). It is therefore desirable to have piezoelectric actuators that are capable of higher volume displacement while having a smaller footprint on the printhead die.